Concrete lifetime, durability, and toughness is limited by its resistance to the formation and coalescence of microscopic cracks in the Portland cement. These are exacerbated by freeze-thaw cycles and water intrusion/migration. By itself, concrete has a limited local fracture resistance owing to little energy being consumed by damage in the volume of material around a brittle failure.
Fibrous reinforcement may be used for improving the physical properties of cement and concrete structures, such as for the production of pipes, corrugated boards, roofing slates, machine foundations, storage tank walls, reactors, aircraft runways, roads, pilings and many other high strength articles.
Of the fibers currently used for cement reinforcement, polyacrylonitrile and polyvinyl alcohol fibers are preferred because they combine high fiber strength with good adhesion to a cement matrix. Unfortunately, both are expensive materials and significantly increase the cost of producing fiber reinforced cement structures. A variety of other less-expensive materials have been considered for production of cement reinforcement fibers.
Steel fibers have been tried and found inadequate because they suffer from chemical attack by the alkaline environment of curing cement. Glass and polyester fibers also degrade due to the alkaline environment of the curing cement matrix. Other polymers, including polyethylene and polypropylene homopolymers, copolymers, or terpolymers have been explored, as have various surfactants for fiber coating. Additionally, fibers made from polymer alloys have been suggested.
However, despite recent advances, there remains an unmet need in the art to optimize concrete with reinforcing fibers which are able to help reduce the formation and propagation of microscopic cracks in concrete.
An embodiment described in examples herein provides a cementitious mixture that includes a mineral cement, and a first population of microfibers. The first population of microfibers includes a first synthetic copolymer including from about 1 mol. % to about 25 mol. % ethylene monomeric units and from about 75 mol. % to about 99.5 mol. % of propylene monomeric units.
Another embodiment described in examples herein provides a process reinforcing a cementitious matrix. The process includes adding a first population of microfibers to a mineral cement to form a cementitious pre-mixture. The first population microfibers includes a first synthetic copolymer that includes from about 1 mol. % to about 25 mol. % of ethylene monomeric units and from about 75 mol. % to about 99.5 mol. % of propylene monomeric units.
Another embodiment described in examples herein, provides a cementitious mixture that includes a mineral cement, a first population of microfibers, and a second population of microfibers. The first population of microfibers includes a first synthetic copolymer that includes from about 1 mol. % to about 25 mol. % of ethylene monomeric units and from about 75 mol. % to about 99.5 mol. % of propylene monomeric units. The second population of microfibers includes a second synthetic copolymer that includes from about 1 mol. % to about 25 mol. % of one of ethylene or propylene monomeric units, and from about 75 mol. % to about 99.5 mol. % of the other of propylene or ethylene monomeric units.